1. Field of the Invention
This invention pertains generally to seating assemblies and more particularly to chairs with devices for occupant temperature control and thermal comfort.
2. Description of Related Art
Thermal comfort of individuals in living or working spaces is typically provided by modifying the temperature of the ambient air and the temperature of the surrounding surfaces in the indoor environment. Heating and cooling systems in a building produce temperature and humidity modified air that is normally distributed to the interior environment through fans and ductwork or through heated or cooled water pumped through radiators in the occupied environment. The comfort of an occupant depends on the rate at which the person exchanges heat with this environment.
The overall heating or cooling of people indoors may occur through four pathways: 1) convective sensible (or ‘dry’) heat transfer between the body surfaces and the surrounding temperature modified air, 2) evaporative heat loss from the skin surface through the clothing and furnishings to the surrounding temperature modified air, 3) radiation exchange with surrounding room and furnishing surfaces, and 4) by conduction to solid surfaces with which the body of the person is in contact. The overall thermal comfort of a person seated in a chair may be determined by one or more of these heat transfer pathways.
However, the rate and efficiency of heat transfers to or from a body and a chair can be negatively influenced by a number of factors. First, because part of the body is in contact with the chair, the body area that is exposed for convection to the temperature modified air is reduced. Second, the evaporation rate of body perspiration may be reduced by vapor resistance imparted by the surface, padding, and structure of the chair, resulting in diminished heat transfer from the body. Third, the chair may block the radiant emissions from the surrounding room surfaces. The chair also may exchange radiation with the person sitting in it, substituting the chair's temperature and radiant emission properties for those of the surrounding room surfaces. Fourth, the chair's conductive properties and thermal capacitance affect the rate of heat transfer out of the seated person when the chair is colder than the clothing temperature, or into the person when the chair is hotter than the clothing temperature. Conductive heat exchange is a prominent effect in vehicular environments which may be much colder or warmer than the person when the person enters the vehicle.
Thermal comfort levels can vary from person to person, typically across a range of about 6 degrees Fahrenheit (3 Kelvin). Consequently, the thermal requirements of some occupants may not be satisfied simply by ambient air temperature control. While the environment may be comfortable to some people, the temperature of the conditioned air or of the environment may be too cold or too hot for other people.
In addition, it may be necessary for the ambient air to be heated or cooled to warmer or colder temperatures than are comfortable in order to accelerate the rate of change of the overall temperature of the environment or of the temperature of the seat. In this setting, the conditioned air is often significantly colder or hotter than the preferred range of comfortable temperatures of an occupant for a period of time, especially at the beginning of the air conditioning cycle. For example, the temperature of a seat in a vehicle or in an enclosed room that has been exposed to the sun for a prolonged period of time can become very hot and may remain hot for a period of time even with exposure to air-conditioned air. It may require the introduction of air that is well below the comfort level of the occupant to the interior of the vehicle to accelerate the rate of cooling of the seat and the environment that air may be uncomfortable for the occupant for a period of time. Likewise, a vehicle seat that has been exposed to winter weather may be very cold and uncomfortable for the occupant requiring the introduction of hot air that greatly exceeds the comfort level of the occupant in order for the rate of temperature change in the seat and interior to be accelerated.
Even with the introduction of extremely conditioned air, the seat temperatures and the perceived interior temperatures may be slow to change because large portions of the body of the occupant of the seat isolate the seat and the body from the heat transfer effects of the conditioned air. Accordingly, the thermal comfort of stationary, seated occupants may not be provided comfortably or efficiently with the introduction of temperature controlled air into the environment.
Therefore, there are situations where a more individualized approach for providing occupant comfort is desirable over simply cooling or heating with temperature modified air. For example, a seat can heat or cool a person with less energy than is possible by heating or cooling the entire ambient space.
To this end, several different types of seats with individualized temperature control systems have been developed. These seats with temperature control systems are typically designed with a perforated seat or seat covering and a source of temperature conditioned air that is passed under pressure through the openings in the surface of the seat to the body of the occupant. Air used in such ‘ventilated seats’ can be ambient air, cooled air or heated air and the airflow across the mesh seat can be in either direction.
One problem experienced by ventilated seat systems is that prolonged exposure to the forced cooled supply air on the body can overcool back muscles and cause back spasms. The contact area of the occupant can also decrease the total flow of air through the seat perforations and diminish the effectiveness of the convection mechanism for heating or cooling the occupant.
Another problem with systems that force air through perforations in the seat surfaces is the need for a relatively high pressure source of temperature modified air, through fans and distribution system that can accommodate the pressure drop across the perforated surface and provide a sufficient air flow.
A further problem with the conventional ventilated seats is the noise that is created by the fans that are part of a pressurized air distribution system that is audible through the surface of the seat. The noise created by the fans, air ducts and air conditioning devices increases with the desired airflow and size of the system to overcome the big pressure drop through the perforated seat surface.
Accordingly, there exists a need for seating with an individualized temperature control system that is efficient, has a low noise level and is effective in heating or cooling the user. The present invention satisfies these needs as well as others and is an improvement in the art.